It is desired to provide an antiulcer agent which exerts effects on suppression of acid secretion as well as protection of gastric mucosa. Known drugs capable of suppressing acid secretion include histamine H.sub.2 receptor blocking drugs such as cimetidine. However, these drugs show no effect on protection of gastric mucosa. Furthermore, they are accompanied by some undesirable side effects on, for example, the central nervous system, which makes them insufficient to be used in preventing or treating ulcer.
Recently, it is known that benzimidazole derivatives such as omeprazole have an intense H.sup.+, K.sup.+ ATPase-inhibitory activity and thus, considerably suppress acid secretion, which would sometimes induce anacidity. Further, these compounds are disadvantageous in that they are unstable to acids and thus frequently decomposed by gastric acid.
Accordingly, it has been urgently required to develop an antiulcer agent which shows well-balanced effects on both suppression of acid secretion and protection of gastric mucosa and has a low toxicity, and is effective for various ulcers and stable against gastric acid.
On the other hand, it is reported that some benzothiazole compounds have H.sup.+, K.sup.+ ATPase-inhibitory and acid secretion-suppressing activities [cf. J. Med. Chem., 31, 1778 (1778 (1988)]. However, the effectiveness of these compounds on various ulcer models have never been reported.